1. Field of the Invention
The present invention relates to a process for commercially producing 5-aminotetrazole suitable for use as an intermediate in the production of gas generants, medicines or pesticides. More specifically, it relates to a process for producing 5-aminotetrazole from cyanamide and hydrazine. The present invention also relates to a method for powdering the 5-aminotetrazole or a metal salt thereof by spray drying.
2. Description of the Related Art
Several processes for producing 5-aminotetrazole are already known in the art. For example, Journal of Organic Chemistry, 15, 1082 (1950) proposes a process for producing 5-aminotetrazole by reacting cyanamide with hydrazoic acid to obtain imidoazide, followed by cyclization or ring formation thereof. This reaction is considered to proceed as follows. ##STR1##
In addition, Journal of Organic Chemistry, 18, 779 (1953) proposes a process for producing 5-substituted tetrazole by reacting a salt of aminoguanidine with nitrite to form a salt of diazoguanidine, followed by cyclization thereof with sodium acetate, sodium carbonate or diluted mineral acid upon heating, as follows. Furthermore, Czechoslovakia Patent No. 190055 (patented Sep. 15, 1981) proposes a process for producing 5-aminotetrazole by reacting aminoguanidine sulfate with nitrite in HCl to form diazoguanidinium chloride, followed by cyclization with sodium acetate upon heating. ##STR2## wherein X represents I, HSO.sub.4 or Cl.
However, since the hydrazoic acid, which is explosive and deadly poisonous, must handle as a starting material in the form of a free acid in the above-mentioned first proposal, special attentions should be paid to materials and sealability of apparatuses, and facilities for treating exhaust gas and waste water, and therefore, this proposal was difficult to be practically used as an industrial scale.
Even in the above-mentioned second proposal, it is necessary to use an expensive salt of aminoguanidine as a starting material. Furthermore, a salt of diazoguanidine, which should be isolated as an intermedial product, is an unstable compound, and therefore, a portion thereof is decomposed to decrease the yield and also the use of the special materials for the apparatuses or the special facilities for the treatment apparatuses etc. Thus, again, this proposal is difficult to be practiced at an industrial scale and is not economical.
On the other hand, the materials capable of forming a salt with a reaction of 5-aminotetrazole include mineral acids, alkali metals, alkaline earth metals, and transition metals. Typical examples of the mineral acids are hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, etc. The alkali metals and alkaline earth metals are mainly used as the hydroxides or oxides for the reaction, typically in the form of sodium hydroxide, potassium hydroxide, magnesium oxide, etc. Typical examples of the transition metals are nickel, zinc, copper, molybdenum, iron, etc. These transition metals are not usually used in the form of the metal per se, but used as the inorganic metal salts or organic metal salts. Examples of the inorganic metal salts are copper chloride and molybdenum chloride, etc. and examples of the organic metal salts are nickel acetate and zinc acetate.
Especially many metal salts of 5-aminotetrazole have high solubilities in water and the other organic solvents. Accordingly, when anhydrous or water-free salts of 5-aminotetrazole are intended to obtain by concentrating the solution containing the above-mentioned metal salts of 5-aminotetrazole, followed by crystallizing, separating and drying the resultant crystals. However, since the solubilities thereof in the solvent are high, there are many cases that the yield of the desired anhydrous salt during the separation step of the crystalline is low and the filtering properties are poor. Furthermore, due to the inherent properties of the materials there are many cases where the hydration is easy to occur. Thus, the drying step thereafter should be sufficiently effected. As mentioned above, the steps of the prior art processes are totally troublesome, and therefore, there are needs that the desired anhydride products can be easily obtained by simply separating and drying the resultant products.
It is considered that the reaction mixture containing the desired metal salts of 5-aminotetrazole is dispersed and crystallized in an organic solvent. However, the use of organic solvents is not preferable from the viewpoints of operation as well as safety and sanitation. In addition, when the organic solvent is recovered, since the new process step is added for this purpose, the production cost is increased.
Azide based conventional gas generants using, for example, sodium azide as a fuel have the problem of the toxicity of the unreacted azide remained. In addition, in the conventional gas generation apparatus, the reaction products formed simultaneously with the generation of gas should be efficiently filtered with a filter.
On the other hand, since conventional non-azide based gas generants are intended to utilize due to their low toxicity, there are disadvantages that the combustion temperature becomes higher, when compared with the case of the azide-based gas generants, and therefore, the combustion temperature is higher than the melting point of the remaining reaction products are difficult to separate by a filter. Therefore, it is intended to modify the form of the reaction products by the addition of an appropriate additive such that the filtration can be effected. It is believed that, to obtain the particles of the reaction product capable of being easily filtered, a high melting point component and an appropriate low boiling point component are coexisted and the high melting point component is fusion coagulated with the low boiling point to thereby form the particles.
The alkali metal salts of 5-aminotetrazole can be a nitrogen gas generating source as a fuel and also can form an appropriate low boiling point component by the reaction with other additives such as silicates or carbonates. Furthermore, the alkali metal salts of 5-aminotetrazole has an effect that the amount of nitrogen oxides (NO.sub.x) generated during the decomposition can be reduced.